Solar collector with expandable fluid mass management system

ABSTRACT

Solar energy conversion systems and methods use solar collectors and working fluid management systems to provide both efficient and safe operation under a wide range of operating conditions. In one embodiment, a solar collector and at least one fluid accumulator preferably with an integral heat exchanger, and at least two mass flow regulator valves enable working fluid flow into and out of the fluid accumulator.

FIELD OF THE INVENTION

The present invention is in the general field of thermodynamics and solar energy conversion.

BACKGROUND OF THE INVENTION

Due to a variety of factors including, but not limited to, global warming issues, fossil fuel availability and environmental impacts, crude oil price and availability issues, alternative energy sources are becoming more popular today. One such source of alternative and/or renewable energy is solar energy. One such way to collect solar energy is to use a solar receiver to focus and convert solar energy into a desired form (e.g., thermal energy or electrical energy). Thermal energy harvested from the sun is known in the art to be utilized in absorption heat pumps, domestic hot water and industrial processes, power generating cycles through the heating of a secondary heat transfer fluid, power generating cycles through the direct heating of power generating working fluid such as steam, and for heating. Furthermore, it is recognized that a wide range of energy consumers can be supplied via electrical and/or thermal energy such as air conditioning, refrigeration, heating, industrial processes, and domestic hot water. Given this, solar collectors that function in efficient manners are desirable.

Traditional solar systems utilize a non-expandable working fluid under pressures less than 50 psia, or working fluids having expandability ratios between the cold and hot temperatures of less than 3. The traditional solar systems utilize a working fluid that is a heat transfer fluid and thus isn't directly compatible as a thermodynamic cycle working fluid. As noted, the density of the working fluid by being expandable changes by an order of magnitude as a function of operating pressure and temperature. Furthermore by definition solar energy is a function of solar intensity and thus at the minimum is absent during the nighttime, unless significant thermal storage is utilized that is currently very expensive, the system will experience substantial changes in density according to operating and ambient conditions.

The combined limitations of each individual component being the solar collector and heat exchangers, pump, heat pump, and fluid control valves presents significant challenges that are further exasperated when seeking to operate the solar collector in a dynamic manner as function of ambient conditions and solar flux.

SUMMARY OF THE INVENTION

The present disclosure and related inventions pertain to solar collectors having an expandable working fluid and an integrated mass management system. The disclosed embodiments utilize gravity to discharge a cooler and more dense fluid as displaced by a volumetrically equivalent warmer and less dense fluid.

In accordance with one aspect of the disclosure and related inventions, there is provided a solar energy conversion system which has a working fluid circuit for receiving and hold a working fluid capable of expansion within the working fluid circuit; at least one solar collector in the working fluid circuit; at least one fluid accumulator in the working fluid circuit; a pump for moving working fluid in the working fluid circuit to the solar collector and to the fluid accumulator; the working fluid circuit also extending between the solar collector and the fluid accumulator, and from the fluid accumulator to the pump.

In accordance with another aspect of the disclosure and related inventions, there is provided a method of converting solar energy acquired from a solar collector and transferred to a working fluid in a working fluid circuit of a solar energy conversion system having at least one solar collector in the working fluid circuit, at least one fluid accumulator in the working fluid circuit, a pump for moving working fluid in the working fluid circuit to the solar collector and to the fluid accumulator, the working fluid circuit also extending between the solar collector and the fluid accumulator, and from the fluid accumulator to the pump, the method including the steps of: controlling the pump to move working fluid through the working fluid circuit to the solar collector and to the fluid accumulator; thermally controlling the fluid accumulator to cool the working fluid in the fluid accumulator; removing working fluid from the fluid accumulator by controlling a valve between the solar collector and the fluid accumulator to an open position when the working fluid has reached a target set point temperature, and controlling a discharge valve between the fluid accumulator and the pump to an open position.

These and other aspects and concepts of the disclosure and related inventions are further described herein in detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sequential flow diagram of one embodiment of an integrated solar collector and inventory mass management system operating with a mechanically driven pressure generating device in accordance with the present invention;

FIG. 2 is a sequential flow diagram of one embodiment of an integrated solar collector and inventory mass management system operating in a hybrid thermosyphon approach in accordance with the present invention;

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the following terms have the respective meanings. The term “in thermal continuity” or “thermal communication”, as used herein, includes the direct connection between the heat source and the heat sink whether or not a thermal interface material is used. The term “fluid inlet” or “fluid inlet header”, as used herein, includes the portion of a heat exchanger where the fluid flows into the heat exchanger. The term “fluid discharge”, as used herein, includes the portion of a heat exchanger where the fluid exits the heat exchanger.

The present invention generally relates to a solar collect system having an integral working fluid management system that enables the system to increase or decrease the mass of the working fluid within the circulation loop of the closed loop system.

Here, as well as elsewhere in the specification and claims, individual numerical values and/or individual range limits can be combined to form non-disclosed ranges.

The heat transfer fluid within the embodiments is preferably a supercritical fluid as a means to reduce the pressure drop within the heat exchanger. The supercritical fluid includes fluids selected from the group of organic refrigerants (R134, R245, pentane, butane), gases (CO2, H2O, He2). A preferred supercritical fluid is void of hydrogen as a means to virtually eliminate hydrogen reduction or hydrogen embrittlement on the heat exchanger coatings or substrate respectively. A preferred supercritical fluid has a disassociation rate less than 0.5% at the operating temperature in which the heat exchanger operates. The specifically preferred heat transfer fluid is the working fluid wherein the combined energy produced (i.e., both thermal, and electrical) displaces the maximum amount of dollar value associated with the displaced energy produced within all of the integrated components including thermodynamic cycle operable within a power generating cycle, vapor compression cycle, heat pump cycle, absorption heat pump cycle, or thermochemical heat pump cycle.

All of the embodiments can be further comprised of a control system operable to regulate the mass flow rate of the working fluid into the solar collector, with the ability to regulate the mass flow rate independently for each pass by incorporating a fluid tank having variable fluid levels optionally interspersed between at least one pass and the other. One method of control includes a working fluid inventory management system. The control system regulates the mass flow rate through methods known in the art including variable speed pump, variable volume valve, bypass valves, and fluid accumulators. The control system is further comprised of at least one temperature sensor for fluid discharge temperature and at least one temperature sensor for ambient air temperature or condenser discharge temperature.

Exemplary embodiments of the present invention will now be discussed with reference to the attached Figures which schematically illustrate the methods and processes disclosed herein, as may be embodied in a device or system for conversion of solar energy into another form of energy or work by use of a working fluid contained in a working fluid circuit made up of conduit for containment and transfer or passage or flow of a working fluid through the conduit and into or through components which are operatively and fluidly connected to the conduit of the working fluid circuit. There may be additional components to the system and the working fluid circuit, such as one or expansion devices, valves, pumps, heat exchangers, recuperators, condensers or other components which are not depicted in the Figures. Such embodiments are merely exemplary in nature. The depiction of solar collectors predominantly as flat panel non-tracking solar absorbers with integral microchannel heat exchangers is merely exemplary in nature and can be substituted by tracking collectors of 1 axis or 2 axis type, vacuum evacuated tubes or panels, switchable configuration between solar absorber or solar radiator mode, low concentration fixed collector, or high concentration tracking collectors. The depiction of pump as a vapor compressor device is merely exemplary and can be substituted with a positive displacement device, a gerotor, a ramjet, a screw, and a scroll. Furthermore, and importantly, the pump can be a turbopump, a positive displacement pump where the selection of the device to increase the working fluid pressure and operate as a mass flow regulator is determined by the density at the inlet pressure and discharge outlet when the incoming working fluid has a density greater than 50 kg per m3, or preferably greater than 100 kg per m3, or specifically greater greater than 300 kg per m3. The depiction of valves as standard mass flow regulators is merely exemplary in nature and can be substituted by variable flow devices, expansion valve, turboexpander, two way or three way valves. The depiction of methods to remove heat from the working fluid as a condenser is merely exemplary in nature as a thermal sink and can be substituted by any device having a temperature lower than the working fluid temperature including absorption heat pump desorber/generator, liquid desiccant dehumidifier, process boilers, process superheater, and domestic hot water. With regard to FIGS. 1 through 2, like reference numerals refer to like parts.

FIG. 1 is a sequential flow diagram of one exemplary embodiment of a solar collector with integral mass management system in accordance with the present invention. In the embodiment of FIG. 1 beginning with the working fluid being discharged from the pump 70, the working fluid can flow either to the solar collector 30 or by way of opening the cold inlet valve 40 a partial stream can enter the expandable fluid accumulator 20. The portion of the working fluid having entered the fluid accumulator 20 is cooled either by ambient exposure of the fluid accumulator exterior at the natural rate realized or accelerated by integrating a heat exchanger 80 directly immersed in the fluid accumulator 20. The heat transfer fluid flowing through the heat exchanger 80 is subsequently cooled by the condenser 50. The working fluid within the fluid accumulator 20 is now at a cooler temperature than when it entered thus for an equivalent pressure the working fluid is more dense. There are disclosed herein two methods to remove working fluid from the fluid accumulator 20 with the first being the use of the solar collector to heat a portion of the working fluid remaining in the main closed loop system by absorbing solar flux and transferring this thermal energy via an embedded heat exchanger within the solar collector 30, and the second being the use of the condenser 50 as a heat source (as compared to the traditional role as a heat sink). Utilizing the first method, the pump 70 prevents backflow during normal operation, and the control system activates the hot inlet valve 10 to the open position when the solar collector 30 has heated the working fluid to a target set point temperature (i.e., achieved a specified density by way of the operating pressure and working fluid temperature). The discharge valve 60 is subsequently opened by the control system to enable the relatively low density and higher temperature working fluid to displace the relatively more dense and lower temperature working fluid. The method of control includes the ability to monitor pump 70 energy consumption by methods known in the art including mass flow meter, kilowatt-hour meter, pump performance maps with a known inlet and discharge pressure, working fluid inlet temperature, and working fluid discharge temperature. The control system can also utilize a database of NIST thermophysical properties to precisely calculate the amount of working fluid within the fluid accumulator 20, or within the closed loop system.

The second method of discharge centers around the condenser 50 operating in reverse mode, thus as a thermal source instead of a thermal sink. Under the second method, the control system will begin the process of using a relatively higher temperature heat transfer fluid into the embedded heat exchanger of the fluid accumulator 20 at which point of reaching either or both the target set point temperature and/or target set point pressure the cold inlet valve 40 is opened (this assumes that the resulting pressure within the fluid accumulator is at least temporarily higher than the closed loop system pressure).

FIG. 2 is a sequential flow diagram of one embodiment of a solar energy conversion system and method which includes one or more solar collectors and one or more fluid accumulators. In the embodiment of FIG. 2, the fluid accumulator 20 discharges directly into the solar collector 30 preferably operating as a thermosiphon, through a discharge valve 60. Beginning with the working fluid at state point A, at least a portion of the working fluid passes through the hot inlet valve 10 when the fluid accumulator is removing working fluid from the main closed loop of the solar collector thermosiphon system, i.e., the working fluid circuit of the solar energy conversion system. As with any thermosiphon system, it is critical that the fluid accumulator 20 be located above the solar collector 30. The expandable working fluid having entered the fluid accumulator 20 is cooled through the heat exchanger 80, which is preferably contained at least partially within the fluid accumulator 20. The heat transfer fluid utilized to cool the working fluid is passed through the accumulator condenser 50.1. The then subsequently cooled working fluid within the fluid accumulator 20 is discharged through the discharge valve 60 back into the solar collector 30, when desired and controlled by a control system to regulate the combination of mass flow rate of the working fluid and the operating pressure of the working fluid within the safe margins of operation. It is understood that temperature sensors can be placed at each state point, including within the fluid accumulator to enable the control system to regulate the flow of working fluid, and heat transfer fluid to remove thermal energy from the working fluid as a means of heating up a thermal sink including domestic hot water, industrial processes, heating, and even power generation.

The right side of FIG. 2 schematically depicts the utilization of a heat transfer fluid that ultimately is heated by a second solar collector 30.1 (which is effectively may be the same as solar collector 30 but showing the relative height of each component to each other) whereby the working fluid removed from the main closed loop transfers a portion of its thermal energy into to increase the density of the stored fluid is conserved by subsequent transfer of the thermal energy to increase from state point T1 as it passes through valve 90 and the fluid accumulator condenser 50.1, now becoming state point D having a temperature sensor T2 100. This stage effectively operates as a preheat of the heat transfer fluid, then passes through the condenser 50 of the main loop now becoming state point E having a temperature sensor T3 110 to continue the flow through the solar collector 30 (or as depicted 30.1). The operation of the solar collector as a thermosiphon requires T1<T2<T3.

It is anticipated that the removal of working fluid from the closed loop system into the fluid accumulator 20 can result from the solar collector operating in essentially a stagnation mode (thus being a safety precaution to limit the solar collector from exceeding it's maximum operating pressure specifications), the closing and/or evacuation of a parallel circuit within the closed loop system, capturing at least a portion of the working fluid “charge” within the closed loop system prior to maintenance of the entire system, enabling the solar collector to operate at relatively higher ambient temperatures, and/or enabling the solar collector to operate at relatively lower operating pressure. The counterpart is the addition of working fluid into the closed loop system from the fluid accumulator 20 as a result of relatively lower ambient temperatures, the opening and/or filling of a parallel circuit within the closed loop system, enabling the solar collector to operate at relatively lower ambient temperatures, and/or enabling the solar collector to operate at relatively higher operating pressure.

It is understood in this invention that a combination of scenarios can be assembled through the use of fluid valves and/or switches such that any of the alternate configurations can be in parallel enabling the solar collector to support a wide range of thermal sinks.

Although the invention has been described in detail with particular reference to certain embodiments detailed herein, other embodiments can achieve the same results.

Variations and modifications of the present invention will be obvious to those skilled in the art and the present invention is intended to cover in the appended claims all such modifications and equivalents. 

1. A solar energy conversion system comprising: a working fluid circuit for receiving and directing flow a working fluid within the working fluid circuit; at least one solar collector in the working fluid circuit; at least one fluid accumulator in the working fluid circuit; a pump for moving working fluid in the working fluid circuit to the solar collector and to the fluid accumulator; the working fluid circuit also extending between the solar collector and the fluid accumulator, and from the fluid accumulator to the pump.
 2. The solar energy conversion system of claim 1 further comprising a cold inlet valve in the working fluid circuit between an output of the pump and the fluid accumulator.
 3. The solar energy conversion system of claim 1 further comprising a discharge valve in the working fluid circuit between the fluid accumulator and an intake of the pump.
 4. The solar energy conversion system of claim 1 further comprising an inlet valve to the fluid accumulator in the working fluid circuit located between the solar collector and the fluid accumulator.
 5. The solar energy conversion system of claim 1 further comprising a heat source in thermal communication with the fluid accumulator.
 6. The solar energy conversion system of claim 5 wherein the heat source is a heat exchanger located at least partially within the fluid accumulator.
 7. The solar energy conversion system of claim 5 further comprising a condenser in thermal communication with the heat source.
 8. The solar energy conversion system of claim 1 further comprising a heat exchanger within the solar collector.
 9. The solar energy conversion system of claim 1 further comprising at least one expansion device in the working fluid circuit.
 10. The solar energy conversion system of claim 1 further comprising a control system operative to control operation of the pump, and to control: the flow of working fluid from the solar collector to the fluid accumulator, the flow of working fluid from the pump to the fluid accumulator, and the flow or working fluid from the fluid accumulator to the pump by reference to operating pressures and working fluid temperatures.
 11. A method of converting solar energy acquired from a solar collector and transferred to a working fluid in a working fluid circuit of a solar energy conversion system having at least one solar collector in the working fluid circuit, at least one fluid accumulator in the working fluid circuit, a pump for moving working fluid in the working fluid circuit to the solar collector and to the fluid accumulator, the working fluid circuit also extending between the solar collector and the fluid accumulator, and from the fluid accumulator to the pump, the method comprising the steps of: controlling the pump to move working fluid through the working fluid circuit to the solar collector and to the fluid accumulator; thermally controlling the fluid accumulator to cool the working fluid in the fluid accumulator; removing working fluid from the fluid accumulator by controlling a valve between the solar collector and the fluid accumulator to an open position when the working fluid has reached a target set point temperature, and controlling a discharge valve between the fluid accumulator and the pump to an open position.
 12. The method of claim 11 further comprising the step of removing working fluid from the fluid accumulator by reference to operating pressure and temperature of the working fluid in the fluid accumulator.
 13. The method of claim 11 further comprising the step of monitoring the energy consumption by the pump by use of a mass flow meter, kilowatt-hour meter, or pump performance map.
 14. The method of claim 11 further comprising the step of calculating an amount of working fluid in the fluid accumulator by reference to a database of NIST thermophysical properties.
 15. A solar energy conversion system comprising: a working fluid circuit for receiving and directing flow of a working fluid within the working fluid circuit; at least one working fluid solar collector in the working fluid circuit; at least one fluid accumulator in the working fluid circuit and located above the solar collector, an inlet an inlet valve in the working fluid circuit connected to an intake of the fluid accumulator, and a discharge valve in the working fluid circuit between the fluid accumulator and the solar collector, and a heat source for controlling a temperature of the fluid accumulator.
 16. The solar energy conversion system of claim 15 wherein the heat source for controlling a temperature of the fluid accumulator is a heat exchanger in thermal communication with the fluid accumulator and with a fluid accumulator condenser.
 17. The solar energy conversion system of claim 15 further comprising a heat transfer fluid circuit connected to the condenser, the heat transfer fluid circuit comprising a heat transfer fluid condenser and a heat transfer fluid solar collector, the heat transfer fluid condenser located below the fluid accumulator condenser and above the heat transfer fluid solar collector.
 18. The solar energy conversion system of claim 15 further comprising an intake valve in the heat transfer fluid circuit proximate to an intake to the fluid accumulator condenser.
 19. A method of converting solar energy acquired from a solar collector and transferred to a working fluid in a working fluid circuit of a solar energy conversion system having at least one working fluid solar collector in the working fluid circuit, at least one working fluid accumulator in the working fluid circuit and means for controlling a temperature of the fluid accumulator, and wherein the solar collector is located below the fluid accumulator whereby the working fluid solar collector operates as a thermosiphon, the method comprising the steps of: controlling introduction of the working fluid into the fluid accumulator by operation of an inlet valve in an inlet in the working fluid circuit to the fluid accumulator; cooling the working fluid in the fluid accumulator; discharging working fluid from the fluid accumulator to the working fluid solar collector according to a desired mass flow rate of the working fluid in the working fluid circuit.
 20. The method of claim 19 wherein the working fluid in the fluid accumulator is cooled by a heat exchanger in thermal communication with a fluid accumulator condenser, by controlling flow of a heat transfer fluid through the fluid accumulator condenser.
 21. The method of claim 20 further comprising the step of heating the heat transfer fluid by a heat transfer fluid solar collector in a heat transfer fluid circuit connected to the fluid accumulator condenser.
 22. The method of claim 21 further comprising the step of passing the heat transfer fluid through a condenser in the heat transfer fluid circuit prior to the heat transfer fluid solar collector.
 23. The method of claim 22 further comprising the step of operating the heat transfer fluid solar collector as a thermosiphon.
 24. The method of claim 19 further comprising the step operating the working fluid solar collector in a substantially stagnant mode.
 25. The method of claim 19 further comprising the step of isolating a flow of a portion of the working fluid through the fluid accumulator and the working fluid solar collector from a remainder of the working fluid circuit.
 26. The method of claim 19 further comprising the step of operating the working fluid solar collector at a temperature relatively higher than an ambient temperature.
 27. The method of claim 19 further comprising the step of operating the working fluid solar collector at a pressure which is relatively lower than a pressure in the working fluid circuit. 